He was born in Port Said, Egypt, to parents of Greek origin, and attended primary and secondary school in Egypt. He graduated from the Theological School of Halki, Istanbul, Turkey in 1939. He did his post-graduate theological studies at Oxford University and at the Sorbonne, Paris.

He took his monastic vows under the name "Parthenios" in 1919, was ordaineddeacon and later priest. He was appointed chief secretary to the Synod of the Patriarchate of Alexandria. From 1953 to 1959, he served as president of the Institute of Oriental Studies of the Patriarchal Library of Alexandria and became a permanent member of the Patriarchal publications. In 1958 he was elected Metropolitan of Carthage in the diocese of Tripoli, Libya, and became a permanent member of the Synod of the Greek Orthodox Patriarchate of Alexandria. In 1968, he was elected member of the Central Committee of the World Council of Churches (WCC), and became a WCC president in 1991.

The patriarch was the author of many theological essays published in numerous international reviews. Patriarch Parthenios III died of a heart attack on July 23, 1996, aged 76, during a visit to Greece. The funeral was held July 30 at the Cathedral Church of St. Nicholas in Cairo, Egypt.